Method for preparing perfluorocarbon-substituted methanols

ABSTRACT

Methods for producing perfluorocarbon monomethanols or dimethanols are disclosed. The methods of the invention can provide branched perfluorocarbon monomethanols or dimethanols with good purity and yields.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of copending U.S. application Ser.No. 10/277,950, filed Oct. 21, 2002, which is a divisional of U.S.application Ser. No. 09/352,554, filed Jul. 13, 1999, now U.S. Pat. No.6,479,712, which is a divisional of application Ser. No. 08/932,763,filed Sep. 17, 1997, now abandoned, which claims priority to ProvisionalApplication No. 60/026,475, filed on Sep. 18, 1996. The contents ofthese documents are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Perfluorocarbon monomethanols, especially perfluoroalkyl monomethanolsrepresented by the general formula CF₃(CF₂)_(n)CH₂OH, are currently usedin various applications. The perfluorocarbon methanols are acidic enoughto chemically adhere to some surfaces to provide slick (low friction)and chemically inert properties. Polymers of acrylic and methacrylicesters derived from perfluorocarbon methanols are used for protectivecoatings which exhibit extremely low surface energy.

Among perfluorocarbon dimethanols, perfluoroalkylene dimethanolsrepresented by the general formula HOCH₂(CF₂)_(n)CH₂OH, are importantintermediates to synthesize various fluoro polymers which are useful ascomponents of protective coatings and paints.

Many commercially available perfluoroalkyl monomethanols andperfluoroalkylene dimethanols possess are of the straight-chainperfluoroalkyl and perfluoroalkylene type. Only a few examples ofbranched perfluoroalkyl monomethanols and perfluoroalkylene dimethanolshave been reported to date. Branched structures generally exhibit lowermelting points than straight-chain structures. For example, 1H,1H-perfluoro-3,7-dimethyl-1-octanol (molecular formula: C₉F₁₉CH₂OH) is afree-flowing liquid at room temperature, while 1H,1H-perfluoro-1-decanol (which has the same molecular formula, but has astraight-chain perfluoroalkyl structure) has a melting point of 82-84°C. Since branched fluoroalkyl groups have multiple perfluoroalkylgroups, they may be able to cover surfaces more effectively thanstraight-chain perfluoroalkyl groups do. The way branchedperfluoroalkylene dimethanols cover surfaces is very similar to that offluoroalkyl acrylates such as perfluoro-1H,1H-octyl acrylate,CF₃(CF₂)₆CH₂OCOCH═CH₂. Fluoropolymers such as poly(perfluoro-1H,1H-octylacrylate) contain relatively long perfluoroalkyl groups extending outfrom the polymer backbone, which provides a highly fluorinated surface.These polymers have been reported to give surfaces which have extremelylow surface tensions (about 10 dyn/cm², Banks, R. E., “OrganofluorineChemicals and Their Industrial Application,” John Wiley & Sons Inc., p216, 1979), much lower than that of polytetrafluorethylene (Teflon)(about 18 dyn/cm²). It is believed that these surface properties are theresult of a tight arrangement of the perfluoroalkyl groups. Though thepolymer backbones (i.e., the polyacrylate polymers) do not contain anyfluorine atoms, they exhibit excellent resistance against weathering,probably due to the protection provided by the perfluoroalkyl groups.Branched perfluorocarbon dimethanols are, therefore, expected to havemany industrial applications.

When a primary perfluorocarboxylic acid ester is reduced, the alkoxygroup (e.g., R in Scheme 1), such as a methoxy (CH₃O—) or ethoxy(CH₃CH₂O—) group, can function as a leaving group when the carbonylgroup is attacked by hydride ion; this results in formation of areactive aldehyde group. Then the intermediate aldehyde can be furtherreduced to give the alcohol as the final reduction product, as shown inScheme 1, in which R_(f) is a perfluorocarbon group.

However, branched perfluoroalkyl groups, such as secondary and tertiaryperfluoroalkyl moieties, sometimes act as pseudo halogens and thereforeare good leaving groups. Because of this, it is very difficult tosynthesize perfluoroalkyl methanols that have branching at the carbonatom next to the CH₂OH group (this carbon atom can be referred to as theα-carbon atom). For example, it has been observed that, in contrast toprimary perfluorocarboxylic acid esters, secondary perfluorocarboxylicacid esters which have branching at the carbon atom next to the carboxylgroup (the α-carbon) may not yield the corresponding branchedperfluoroalkyl methanols when the esters are chemically reduced understandard conditions for the reduction of esters, such as by treatment ofthe ester with lithium aluminum hydride (LAH) or sodium borohydride(NaBH₄). The products of attempted conventional reduction reactions canbe quite complicated. It is believed that when there is a branch site atthe carbon atom next to the carbonyl group, the secondary perfluoroalkylgroup becomes a better leaving group than the alkoxy group because ofthe two strong electron withdrawing perfluoroalkyl groups. Thus, thesecondary perfluoroalkyl group becomes a leaving group upon attack byhydride ion on the carboxylic ester functionality, producing aperfluoroalkyl anion and a formate ester, as shown in Scheme 2, in whichR is an alkyl group and R_(f) and R′_(f) are perfluoroalkyl groups.

The formate ester may then be further reduced. The perfluoroalkyl anioncan rapidly decompose into an olefin (Scheme 3), which can react furtherwith the reducing reagent or with solvent to give a complicated productmixture.

Possibly for the above-described reasons, there are few reports ofsyntheses of perfluorocyclohexylmethanol compounds by reduction of thecorresponding esters. In one of the few successful preparations,(perfluorocyclohexyl)methanol was successfully prepared by the reductionof perfluorocyclohexanecarboxylic acid fluoride with sodium borohydride(Scheme 4; the “F” in the cycloalkyl ring in Scheme 4 indicates that thecyclohexyl ring is perfluorinated) (Gambaretto, Giampaolo, et al. Att.Ist. Veneto Sci., Lett. Arti. Cl. Sci. Mat. Nat. 1973, 132, 289-93; C.A.83, 163685e). However, this procedure may require the synthesis of thecorresponding carboxylic acid, followed by conversion to the acid halide(e.g., acid fluoride. Such a two-step procedure can be cumbersome andinefficient.

Similarly, perfluoropolyether alkyl methanols were synthesized as shownin Scheme 5 (Vilenchik, Ya. M.; Lekentseva, G. I. 'neifel'd, P. G. andPospelova, N. B., Zh. Vses. Khim. O-va. 1981, 26(2), 212-3. ; C.A. 95,96946y).

Certain perfluoropolyethers (e.g., as shown in Scheme 5) haveperfluoroalkoxy groups directly attached to the carbon atom next to thecarbonyl group (the α-carbon). Perfluoroalkoxy groups generally do nothave as strong an electron withdrawing effect as perfluoroalkyl groups,possibly because of the electron rich oxygen atom, and may thereforemake a perfluoroalkylene group which is substituted with theperfluoroalkoxy moiety a poorer leaving group than a correspondingperfluoroalkyl group. Thus, while poor results are often obtained uponreductive treatment of branched (perfluoralkyl) carboxylic methyl esters(e.g., Scheme 2, in which R is a methyl group, see supra),perfluoropolyether methanols can be prepared by the reduction of alkylesters (e.g., methyl esters, as shown in Scheme 6) (Tamaru, Sinji,European Patent Application No. EP 79,590).

SUMMARY OF THE INVENTION

The present invention relates to methods for producingperfluorocarbon-substituted methanols, including straight- andbranched-chain perfluoralkylmethanols, straight- and branched-chainperfluoroalkylene dimethanols, and perfluorocycloalkyl methanols. Themethod also provides novel perfluorocarbon-substituted methanols,including straight- and branched-chain perfluoralkylmethanols, straight-and branched-chain perfluoroalkylene dimethanols, andperfluorocycloalkyl methanols. The invention further providesperfluorocarbon-substituted methanols prepared according to the methodsof the invention.

In one embodiment, the invention provides a method for preparing aperfluorocarbon methanol. The method includes reacting a perfluorocarbonester of a perfluorocarbon carboxylic acid with a reducing reagent underreducing conditions, such that a perfluorocarbon methanol is prepared.The perfluorocarbon ester of a perfluorocarbon carboxylic acid can berepresented by the formula R_(f)—C(O)OR″_(f), in which R_(f) and R″_(f)are each independently a substituted or unsubstituted perfluoroalkylgroup. In certain embodiments, R″_(f) can be-CF₂R′″_(f), in whichR′″_(f) is a perfluoroalkyl group. In some embodiments, theperfluorocarbon methanol can be represented by the formulaR_(f)—CF(R′_(f))—CH₂OH, in which R_(f) and R′_(f) are each independentlyperfluoroalkyl. In certain embodiments, the perfluorocarbon ester of aperfluorocarbon carboxylic acid is a lactone. In certain embodiments,the reducing reagent comprises a metal hydride, while in otherembodiments, the reducing reagent comprises a hydrogen source and acatalyst, such as a noble metal catalyst selected from the groupconsisting of a platinum catalyst and a palladium catalyst.

In another aspect, the invention provides a method for preparing acompound represented by the formula R_(f)—CH₂OH, in which R_(f) is amoiety selected from the group consisting of perfluoroaliphatic moietiesand perfluoroaryl moieties. The method includes reacting aperfluorocarbon ester of a perfluorocarbon carboxylic acid representedby the formula R_(f)—COOR″_(f), in which R″_(f) is perfluoroaliphatic orperfluoroaromatic, with a reducing reagent under reducing conditions,such that a compound represented by the formula R_(f)—CH₂OH is prepared.

In another embodiment, the invention provides a perfluorocarbon methanolcompound having a hydroxymethyl group and an carbon atom attached to thehydroxymethyl group, wherein the carbon atom attached to thehydroxymethyl group is substituted with at least one perfluorocarbonmoiety, with the proviso that the compound is not(perfluorocyclohexyl)methanol and with the further proviso that thecarbon atom attached to the hydroxymethyl group is not substituted witha perfluoroalkoxy moiety.

In another aspect, the invention provides a compound selected from thegroup consisting of perfluoro-1H,1H-2-hexyldecanol,2-fluoro-2-perfluorooctyl-1,3-propanediol,2-fluoro-2-perfluorobutyl-1,3-propanediol, perfluoro 1H,1H,4H-undecane1,4-diol, and perfluoro 1H,1H,5H-dodecan-1,4-diol.

In another embodiment, the invention provides a perfluoro1H,1H,nH-alkyl-1,n-diol, in which the alkyl moiety includes from 3 to 15carbon atoms, and n is an integer from 3 to 15.

In another aspect, the invention provides a perfluoroalkyl methanolcompound represented by the formula HOCH(R_(f))—R′_(f)—CH₂OH, whereinR′_(f) is a substituted or unsubstituted perfluorocarbon moiety andR_(f) is a substituted or unsubstituted perfluorocarbon moiety. R′_(f)can be an unsubstituted or substituted divalent, perfluorinated, alkylor alkenyl organic radical having one to twenty fully fluorinated carbonatoms, which radical can be interrupted by divalent oxygen or sulfuratoms, and R_(f) can be a substituted or unsubstituted perfluoroalkylmoiety.

In another embodiment, the method provides a perfluorocarbon dimethanolcompound represented by the formula R_(f)—C(R′_(f))(CH₂OH)₂, whereinR_(f) and R′_(f) are each independently a substituted or unsubstitutedperfluorocarbon moiety. R_(f) and R′_(f) can each independently be anunsubstituted or substituted monovalent, perfluorinated, alkyl oralkenyl organic radical having one to twenty fully fluorinated carbonatoms, which radical can be interrupted by divalent oxygen or sulfuratoms.

In still another embodiment, the invention provides a perfluoroalkylmethanol prepared by the methods of the invention.

DETAILED DESCRIPTION OF THE INVENTION

For convenience, certain terms used throughout the specification andclaims are defined.

The term “perfluorocarbon”, as used herein, refers to a moiety whichincludes a carbon backbone which is substituted with one or morefluorine atoms, and which preferably does not include any covalent bondsbetween carbon and hydrogen. Exemplary perfluorocarbons includeperfluorinated monovalent aliphatic groups (including perfluoroalkyls,alkenyls, and alkynyls) and perfluorinated aryl groups (such as phenyl,pyridinyl, and the like), as well as divalent groups such asperfluoroalkylene, perfluoroalkenylene, perfluoroalkynylene, andperfluoroarylene (e.g., 1,4-phenylene). A preferred monovalentperfluorocarbon is a perfluoroalkyl, while a preferred divalentperfluorocarbon is perfluoroalkylene. A perfluorocarbon moiety such as aperfluoroalkyl can often be prepared from a correspondingnon-fluorinated moiety, e.g., a hydrocarbyl moiety, by perfluorination,e.g., according to reported methods for perfluorination. It will beappreciated, however, that perfluorination may destroy certainfunctionalities, such as olefins, and perfluorination of, e.g.,alkenyls, may be difficult. Perfluorocarbons can be straight orbranched-chain, or cyclic, and can be unsubstituted or substituted asdescribed hereinafter.

The term “perfluorocarbon-substituted methanol” is a methanol having atleast one hydrogen atom replaced by a perfluorocarbon moiety. Thus, aperfluorocarbon-substituted methanol can be represented by the formulaR_(f)—CH₂OH, in which R_(f) is a perfluorocarbon moiety (preferably aperfluoroalkyl moiety). It will be appreciated that, in certainembodiments, the hydrogen atoms of a perfluorocarbon-substitutedmethanol (i.e., in the moiety —CH₂OH) can be deuterium or tritium atoms.Preferred perfluorocarbon-substituted methanols can be represented bythe formula

in which R₁, R₂, and R₃ are each independently selected from the groupconsisting of fluorine, straight- or branched-chain perfluoro aliphaticmoieties (including substituted or unsubstituted perfluoroalkyls,perfluoroalkenyls, and perfluoroalkynyls) and perfluoroaryls. Inpreferred embodiments, at least one of R₁, R₂, and R₃ is a perfluoralkylgroup. In preferred embodiments, at least one of R₁, R₂, and R₃ is not afluorine atom; in particularly preferred embodiments, at least two ofR₁, R₂, and R₃ are not fluorine atoms; in this instance, theperfluorocarbon-substituted methanol is branched at the α-carbon (thecarbon atom to which R₁, R₂, and R₃ are attached). In embodiments inwhich at least one of R₁, R₂, and R₃ is a substituted perfluoroalkylgroup, a preferred substituent of the substituted perfluoroalkyl is aperfluoroalkoxy group.

The term “perfluorocarbon dimethanol” refers to a compound having aperfluorocarbon moiety which is substituted with two hydroxymethyl(CH₂OH) groups. Thus, a perfluorocarbon dimethanol can be represented bythe formula HOCH₂—R_(f)—CH₂OH, in which R_(f) is a straight- orbranched-chain perfluoroalkylene, perfluoroalkenylene,perfluoralkynylene, or perfluoroarylene group (such as phenylene,pyridinylene, naphthalenylene (i.e., —C₁₀F₆-), and the like);perfluoroaliphatic groups (particularly perfluoroalkylene groups) arepreferred.

The term “perfluorocarbon polymethanol” refers to a compound having aperfluorocarbon moiety substituted with at least three hydroxymethyl(CH₂OH) groups.

The language “perfluoroalkyl ester of a perfluoroalkyl carboxylic acid”refers to a compound having the formula R_(f)—C(O)OR″_(f), in whichR_(f) and R″_(f) are perfluoroalkyl groups (which may be the same ordifferent, branched or straight, and substituted or unsubstituted); orR_(f) and R″_(f), taken together with the carboxyl group to which theyare attached, form a cyclic ester (a lactone). In another preferredembodiment, R″_(f) is a primary perfluoroalkyl group, i.e., —CF₂R′″_(f),in which R′″_(f) is a perfluoroalkyl group. A “perfluoralkyl carboxylicacid” can be represented by the formula R_(f)—C(O)OH, R_(f) is aperfluoroalkyl group (which may be branched or straight, and substitutedor unsubstituted). It will be appreciated that the term “perfluoroalkylester of a perfluoroalkyl carboxylic acid” is employed for convenienceand is not intended to suggest that such an ester is necessarilyprepared by esterification of a perfluoroalkyl carboxylic acid. Indeed,in certain embodiments, a “perfluoroalkyl ester of a perfluoroalkylcarboxylic acid” can be prepared by perfluorination of an alkyl ester(of a carboxylic acid) (see, e.g., the Examples, infra). The term“perfluorocarbon ester of a perfluorocarbon ester of a carboxylic acid”refers to a compound having the formula R_(f)—C(O)OR″_(f), in whichR_(f) and R″_(f) are perfluorocarbon groups (which may be the same ordifferent, branched or straight, and substituted or unsubstituted); orR_(f) and R″_(f), taken together with the carboxyl group to which theyare attached, form a cyclic ester (a lactone).

The term “alkyl” refers to the radical of saturated aliphatic groups,including straight-chain alkyl groups, branched-chain alkyl groups,cycloalkyl (alicyclic) groups, alkyl substituted cycloalkyl groups, andcycloalkyl substituted alkyl groups. In preferred embodiments, astraight chain or branched chain alkyl has 30 or fewer carbon atoms inits backbone (e.g., C₁-C₃₀ for straight chain, C₃-C₃₀ for branchedchain), and more preferably 20 or fewer. Preferred cycloalkyls have from4-10 carbon atoms in their ring structure, and more preferably have 5, 6or 7 carbons in the ring structure. A perfluoroalkyl group is an alkylgroup in which all C—H bonds are replaced by C—F bonds.

Moreover, the term “alkyl” as used throughout the specification andclaims is intended to include both “unsubstituted alkyls” and“substituted alkyls”, the latter of which refers to alkyl moietieshaving substituents replacing a hydrogen on one or more carbons of thehydrocarbon backbone. Such substituents can include, for example,halogen, hydroxyl, alkoxyl, cyano, heterocyclyl, aralkyl, or an aromaticor heteroaromatic moiety. It will be understood by those skilled in theart that the moieties substituted on the hydrocarbon chain canthemselves be substituted, if appropriate. Cycloalkyls can be furthersubstituted, e.g., with the substituents described above. An “aralkyl”moiety is an alkyl substituted with an aryl (e.g., phenylmethyl(benzyl)). A perfluoroalkyl moiety can be substituted with substituentsas described for alkyl groups, although such substituents are preferablyperfluorinated. Exemplary perfluoroalkyl groups include trifluoromethyl,pentafluoroethyl, heptafluoroisopropyl, 2-trifluoromethoxyperfluoropentyl, perfluorocyclopentyl, and the like.

The term “aryl” as used herein includes 5- and 6-membered single-ringaromatic groups that may include from zero to four heteroatoms, forexample, benzene, pyrrole, furan, thiophene, imidazole, oxazole,thiazole, triazole, pyrazole, pyridine, pyrazine, pyridazine andpyrimidine, and the like. Aryl groups also include polycyclic fusedaromatic groups such as naphthyl, quinolyl, indolyl, and the like. Thearomatic ring can be substituted at one or more ring positions with suchsubstituents as described above, as for example, halogen, hydroxyl,alkyl, alkoxy, cyano, azido, heterocyclyl, alkyl, aralkyl, or anaromatic or heteroaromatic moiety. Aryl groups can also be fused orbridged with alicyclic or heterocyclic rings which are not aromatic soas to form a polycycle (e.g., tetralin). A perfluoroaryl group can besubstituted with substituents as described for aryl groups, athough suchsubstituents are preferably perfluorinated.

The terms “alkenyl” and “alkynyl” refer to unsaturated aliphatic groupsanalogous in length and possible substitution to the alkyls describedabove, but that contain at least one double or triple bond respectively.

Unless the number of carbons is otherwise specified, “lower alkyl” asused herein means an alkyl group, as defined above, but having from oneto ten carbons, more preferably from one to six carbon atoms, in itsbackbone structure. Likewise, “lower alkenyl” and “lower alkynyl” havesimilar chain lengths. Preferred alkyl groups are lower alkyls.

The term “reducing agent” is art-recognized and is intended to includeany agents which are capable of converting a carbonyl group into thecorresponding alcohol. A variety of reducing agents are well known tothe ordinarily skilled artisan (for example, see, e.g., R. Larock,“Comprehensive Organic Transformations”, VCH Publishers, Inc., 1989).Examples of preferred reducing agents include sodium borohydride,lithium borohydride, lithium aluminum hydride, and diborane. Catalytichydrogenation (e.g., with a metal catalyst such as palladium (e.g.,palladium on carbon or tetrakis(triphenylphosphine)palladium(0)),platinum (e.g., platinum on carbon), or rhodium (e.g.,tetrakis(triphenylphosphine)rhodium(I) chloride), or the like, can alsobe employed with a suitable hydrogen donor source. Examples of hydrogensources include hydrogen gas (e.g., a catalytic reduction performedunder an atmosphere of hydrogen gas), cyclohexene, and the like.

I. Methods

In one aspect, the invention relates to methods for preparingperfluorocarbon-substituted methanols. The methods of invention allowsynthesis of straight- or branched-chain perfluorocarbon-substitutedmethanols, dimethanols, and polymethanols, which can be difficult toprepare by conventional methods. The methods of the invention are alsoapplicable to the synthesis of branched perfluorocarbon dimethanols.Such branched fluoro compounds are believed to possess improvedsurface-modifying properties, such as lowered surface energy, enhancedchemical stability, increased UV stability and so on, compared tostraight-chain fluoro compounds, due to the ability of branchedperfluoro compounds to cover surfaces more effectively thanstraight-chain compounds.

According to the present invention, there is provided a method ofproducing straight- or branched-chain perfluorocarbon monomethanols ordimethanols (or, in certain cases, polymethanols). The method involvesthe reduction of perfluorinated carboxylic acid esters or diesters (orgreater numbers of ester moieties) to provide the correspondingperfluorocarbon methanols. The methods of the invention provide accessto compounds which have heretofore been difficult to obtain in goodyield. Moreover, in preferred embodiments, the methods of the inventionprovide the desired perfluorocarbon methanol compounds in a single stepfrom readily prepared stable starting materials, often in high yield.Thus, the invention provides a simple, rapid, relatively inexpensive andquite general method for the preparation of a variety of perfluorocarbonmethanol compounds.

The methods of the invention are based, at least in part, on theunderstanding that the leaving group (such as Y in Scheme 7) of aperfluorocarbon carboxylic acid derivative I should, in general, be abetter leaving group than the secondary or tertiary perfluoroalkyl groupin order to successfully synthesize alpha branched perfluoroalkylmethanols II as illustrated in Scheme 7.

It has now been found that reduction of compounds such as compound I, inwhich Y is a perfluorocarbon group, such as a perfluoroalkoxy orperfluoroaryloxy moiety (e.g., R″_(f)O—, in which R″_(f) is aperfluoroalkyl or perfluoroaryl group, more preferably a perfluoroalkylgroup) can be accomplished smoothly and in good to excellent yield undersimple conditions. Since perfluoroalkoxy groups are generally betterleaving groups than perfluoroalkyl groups, the reduction reactionproceeded smoothly to yield perfluorocarbon monomethanols or dimethanolseven when there was a branch site at the carbon atom next to thecarbonyl group.

An exemplary reaction scheme for the reduction of a perfluoroalkyl esterof a perfluoroalkyl carboxylic acid is shown in Scheme 8.

Without wishing to be bound by theory, it is believed that initialhydride attack at the carbonyl group of III (in which R_(f) and R″_(f)are both perfluorocarbon (e.g., perfluoroalkyl) moieties, which can bethe same or different) initially yields a perfluoroalkanal (aldehyde) IVand a perfluoroalkoxide ion V. The perfluoroalkanal IV is furtherreduced to the perfluorocarbon (e.g., perfluoroalkyl) methanol VI.Perfluoroalkoxide ion V, on the other hand, immediately decomposes intoperfluorocarboxylic acid fluoride VII and fluoride ion. Since thefluoride group is a very good leaving group, as mentioned supra, theperfluorocarboxylic acid fluoride VII can be reduced (viaperfluoroaldehyde VIII) to another perfluoroalkyl methanol IX even ifthe group R″_(f) is a secondary or tertiary perfluoroalkyl group.

In Scheme 8, the leaving group (corresponding to Y in Scheme 7) has theformula —OCF₂R″_(f). The resultant fluoroalkoxide decomposes to producea perfluorocarbon methanol. However, it will be appreciated that otherperfluorinated moieties can serve as leaving groups, and other productscan be expected. For example, if Y in Scheme 7 has the formula—OCF(R_(1f))(R_(2f)), in which R_(1f) and R_(2f) are eachperfluorocarbon moieties, decomposition of the released fluoroalkoxidewill yield a ketone, which can be reduced under the reaction conditionto yield a compound of the formula R_(1f)CH(OH)—R_(2f). If Y in Scheme 7is a trifluoromethyl group, the product after ester cleavage,decomposition to carbonyl fluoride, and reduction, is methanol. If Y inScheme 7 is a tertiary group (i.e., —OC(R_(1f))(R_(2f))(R_(3f)), inwhich R_(1f), R_(2f) and R_(3f) are each perfluorocarbon moieties, theproduct after ester cleavage, is HOC(R_(1f))(R_(2f))(R_(3f)). Thus, theleaving group moiety can be selected to provide a desired product oravoid undesired products.

It can be seen from Scheme 8 that the reduction of one mole ofperfluorinated ester gives two moles of perfluoroalkyl methanols (onemole each of R_(f)CH₂OH and R″_(f)CH₂OH). It will be appreciated thatone mole of a compound of formula III, in which R_(f) and R″_(f) areidentical, can be reduced to provide two moles of the desired productR_(f)CH₂OH. This represents a highly efficient synthesis with littlewasted material. It will also be appreciated that reduction of aperfluoroester compound having the formula R_(f)C(O)OCF₂R″_(f) canprovide the same products after reduction as the compoundR″_(f)C(O)OCF₂R_(f). For example, reduction of perfluoro(ethyl2-methylpropionate) (formula CF₃CF(CF₃)C(O)OCF₂CF₃) provides the sameproducts as does reduction of perfluoro(2-methylpropyl acetate) (formulaCF₃C(O)OCF₂CF(CF₃)CF₃); in each case, perfluroisopropylmethanol(perfluoro 1H,1H-sec-butanol) and trifluoromethylmethanol(2,2,2-trifluoroethanol). Thus, it is often possible to select from twoperfluorinated esters as starting materials for reduction to provide thedesired product or products. The more readily available, or less costly,starting material can then be employed.

The methods of the invention also provide access to a wide variety ofstraight- and branched-chain perfluoroalkylene or perfluorarylenedimethanols. For example, perfluoroalkylene or perfluorarylenedimethanols can be prepared by the hydride reduction of perfluorinatedesters. In one embodiment, a perfluorinated alkylene or arylene diesteris reduced to provide a perfluoroalkylene or arylene dimethanol. Thus,for example, in one embodiment, reduction of a compound represented bythe formula R″_(f)C(O)OCF₂R_(f)CF₂OC(O)R″_(f), in which R_(f) is aperfluoroalkylene or perfluorarylene moiety, and each R″_(f) is aperfluorocarbon group which may be the same or different (e.g., aperfluoralkyl or perfluoroaryl group), provides a perfluorodimethanol ofthe formula HOCH₂R_(f)CH₂OH along with two equivalents of R″_(f)CH₂OH).The starting material can be readily prepared from a diol of the formulaHOCH₂RCH₂OH (a variety of which are commercially available) byesterification under standard conditions with a carboxylic acid of theformula R″COOH (or a derivative thereof), to yield a diester of the formR″C(O)OCH₂RCH₂OC(O)R″ (R and R″ are the non-fluorinated analogs of R_(f)and R″_(f)). Note that the non-fluorinated diol HOCH₂RCH₂OH andnon-fluorinated carboxylic acid R″COOH can be employed instead of thefluorinated (and likely more expensive) HOCF₂R_(f)CF₂OH and R″_(f)COOH,although the fluorinated compounds could be used if desired. The diesterR″C(O)OCH₂RCH₂OC(O)R″ can then be perfluorinated by methods known in theart (e.g., see infra) to provide the diesterR″_(f)C(O)OCF₂R_(f)CF₂OC(O)R″_(f) for reduction.

In another embodiment, reduction of a compound represented by theformula R″_(f)CF₂OC(O)R_(f)C(O)OCF₂R″_(f), in which R_(f) is aperfluoroalkylene or perfluorarylene moiety and each R″_(f) is aperfluoroaliphatic or perfluoraryl moiety, provides aperfluorodimethanol of the formula HOCH₂R_(f)CH₂OH (along with twoequivalents of R″_(f)CH₂OH). It will be appreciated that the products ofreduction are the same as in the previous instance. The perfluorodiester R″_(f)CF₂OC(O)R_(f)C(O)OCF₂R″_(f) can be prepared byesterification of a diacid HOC(O)RC(O)OH with a suitable alcohol R″CH₂OH(R and R″ are the non-fluorinated analogs of R_(f) and R″_(f)), toprovide a diester, followed by perfluorination of the diester to producethe required perfluorinated diester.

The methods of the invention also contemplate reduction ofperfluoroaliphatic lactones (cyclic esters) to produce diols. Forexample, reduction of a gamma lactone can provide a perfluoroalkyl1,4-butane diol, as depicted in Scheme 9, below.

As depicted in Scheme 9, perfluoroalkyl-substituted 1,4-butanediols canbe synthesized conveniently from commercially available gamma lactones(see Example 6, infra). Perfluorination of the gamma lactone provides aperfluorinated lactone (R_(f) is a perfluorinated substituent) which isrecued to provide a ring-opened intermediate fluoroalkoxide-aldehyde.The fluoroalkoxide decomposes to a ketone, and both the ketone and esterfunctionalities are reduced to provide a perfluoro 1H,1H,4H-alkyl1,4-diol. Fluorinated 1,5-pentanediols can be similarly prepared fromdelta lactones (see Example 7, infra). Other unsubstituted orsubstituted lactones, having from 4 to 16 atoms in the ring, morepreferably 4 to 9 atoms in the ring, still more preferably from 5 to 7atoms in the ring, can be employed. Thus, the invention provides asimple route to perfluoro 1H,1H,nH-alkyl 1,n-diols, in which n is aninteger from 3 to 15, more preferably 3 to 8, and more preferably 4 to 6atoms in the ring.

As described above, the present invention provides a straightforwardmethod to synthesize a wide variety of branched perfluorocarbonmonomethanols and dimethanols. The starting perfluorinated carboxylicacid esters and diesters can be prepared directly from the correspondinghydrocarbon esters by liquid phase fluorination such as the onedescribed by Bierschenk et al (U.S. Pat. No. 5,093,432).

The reactions of the present invention may be performed under a widerange of conditions, though it will be understood that the solvents andtemperature ranges recited herein are not limitative and only correspondto a preferred mode of the process of the invention. The reactionconditions (temperature, choice of solvent, choice of reducing agent orcatalyst, order of addition of reagents, etc.) can be selected accordingto factors well known to one of ordinary skill in the art. In preferredembodiments, the particular reducing agent employed can be selected toreduce a carboxylic ester functionality of a perfluorinated ester, whileminimizing concomitant reduction of other functional groups (if any)present in the starting materials or desired products. For example, ifthe starting ester and desired product include an olefinic (double bond)functionality, it is preferred to select a reducing agent, and otherreaction conditions, such that reduction of the double bond isminimized.

In certain preferred embodiments, a reduction reaction is carried outgenerally by adding a perfluorinated ester to a mixture containing asolvent and a reducing agent. The perfluorinated ester can be addeddirectly (neat) to the reaction vessel, or after being diluted with adiluent, e.g., for ease of handling. Various diluents can be employed.Suitable diluents include perfluorinated hydrocarbons,chlorofluorocarbons, bromofluorocarbons and perfluoroethers. Onepreferred diluent is Halocarbon oil 0.8™ (an oligomer ofchlorotrifluoroethylene) (available from Halocarbon Products Corp.).

Reduction reactions according to the invention are preferably conductedin a fluid medium, e.g., in suspension or solution in a solvent. Avariety of solvents are suitable; preferred solvents include ethers suchas diethyl ether, tetrahydrofuran, dioxane and diglyme. In general, asolvent should be selected to avoid unwanted reaction with the startingester or the reducing agent. For example, a protic solvent such as analcohol should generally not be employed in conjunction with a highlyreactive reducing agent such as lithium aluminum hydride. A suitablesolvent can be selected by one of ordinary skill in the art using nomore than routine experimentation in light of the teachings herein.

In general, reactions according to the invention can be performed over arange of temperatures from about −80° C. up to the boiling point of thesolvent or solvent mixture employed. In general, reactions will beusually be run at temperatures in the range of −78° C. to 150° C., morepreferably in the range −20° C. to 100° C. When sodium borohydride isused as a reducing agent, reaction temperatures preferably range betweenabout −20° C. and 100° C., and more preferably between about 10° C. and60° C.

In certain embodiments it is preferable to perform the reactions underan inert atmosphere of a gas such as nitrogen or argon.

In certain instances, the reactions of the invention can producefluoride ion as a byproduct. Fluoride ion can be destructive to glassvessels, so in certain embodiments it is advantageous to employ plasticor plastic-coated reaction vessels to avoid such damage.

II. Compounds

In another aspect, the invention provides novel perfluorocarboncompounds. The invention provides compounds having a variety ofstructures, including perfluorocarbon methanols and dimethanols, inwhich the fluorocarbon moiety can be cyclic, straight, or branched.Perfluorocarbon methanols are well known for surface modification. Ithas been reported that certain perfluorocarbon diols are useful forpreparation of water-repellent protective materials (see, e.g., U.S.Pat. Nos. 3,935,277, 3,968,066, 4,046,944, 4,054,592, 4,098,742,4,946,992, 5,663,273), including polyurethanes.

In one embodiment, the invention provides a perfluorocarbon methanolcompound having a hydroxymethyl group and an carbon atom attached to thehydroxymethyl group, wherein the carbon atom attached to thehydroxymethyl group is substituted with at least one perfluorocarbonmoiety, with the proviso that the compound is not(perfluorocyclohexyl)methanol and with the further proviso that thecarbon atom attached to the hydroxymethyl group is not substituted witha perfluoroalkoxy moiety. Thus, in one embodiment, the compound can berepresented by the formula

in which R₁ and R₂ are each independently selected from the groupconsisting of straight- or branched-chain perfluoro aliphatic moieties(including substituted or unsubstituted perfluoroalkyls,perfluoroalkenyls, and perfluoroalkynyls) and perfluoroaryls, and R₃ isselected from the group consisting of fluorine, straight- orbranched-chain perfluoro aliphatic moieties (including substituted orunsubstituted perfluoroalkyls, perfluoroalkenyls, and perfluoroalkynyls)and perfluoroaryls; with the proviso that the compound is not(perfluorocyclohexyl)methanol. In this embodiment, theperfluorocarbon-substituted methanol is branched at the α-carbon (thecarbon atom to which R₁, R₂, and R₃ are attached). In preferredembodiments, at least one of R₁ and R₂ is a perfluoralkyl group. Inembodiments in which at least one of R₁, R₂, and R₃ is a substitutedperfluoroalkyl group, a preferred substituent of the substitutedperfluoroalkyl is a perfluoroalkoxy group.

In another embodiment, the invention provides the compoundsperfluoro-1H,1H-2-hexyldecanol,2-fluoro-2-perfluorooctyl-1,3-propanediol,2-fluoro-2-perfluorobutyl-1,3-propanediol, perfluoro1H,1H,4H-undecane1,4-diol, and perfluoro 1H,1H,5H-dodecan-1,4-diol. The synthesis ofthese compounds is detailed in the Examples, infra.

In another embodiment, the invention provides perfluoro 1H,1H,nH-alkyl1,n-diols, in which the perfluoralkyl moiety is straight- orbranched-chain, substituted or unsubstituted. The perfluoralkyl chainpreferably includes from 3 to 15 carbon atoms, and n is an integer from3 to 15, more preferably 3 to 8, and more preferably 4 to 6 atoms in thering. As described above, the perfluoro 1H,1H,nH-alkyl 1,n-diols can beprepared by reduction of perfluoralkyl lactones.

In another embodiment, the invention provides a perfluorocarbon methanolcompound represented by the formula HOCH(R_(f))—R′_(f)CH₂OH, whereinR′_(f) is a substituted or unsubstituted perfluorocarbon moiety andR_(f) is a substituted or unsubstituted perfluorocarbon moiety. Inpreferred embodiments, R′_(f) is an unsubstituted or substituteddivalent, perfluorinated, alkyl or alkenyl straight, branched or cyclicorganic radical having one to twenty (more preferably one to ten) fullyfluorinated carbon atoms, which radical can be interrupted by divalentoxygen or sulfur atoms. In certain embodiments, R_(f) is a substitutedor unsubstituted perfluoroalkyl moiety having from one to twenty (morepreferably one to ten) carrbon atoms in the perfluoralkyl chain.

In yet another embodiment, the invention provides a perfluorocarbondimethanol compound represented by the formula R_(f)—C(R′_(f))(CH₂OH)₂,wherein R_(f) and R′_(f) are each independently a substituted orunsubstituted perfluorocarbon moiety. In certain embodiments, R_(f) andR′_(f) are each independently an unsubstituted or substitutedmonovalent, perfluorinated, alkyl or alkenyl organic radical having oneto twenty fully fluorinated carbon atoms, which radical can beinterrupted by divalent oxygen or sulfur atoms.

In still another embodiment, the invention provides perfluorcarboncompounds prepared by the any of the methods of the invention asdescribed herein

The present invention is further illustrated by the followingnon-limiting examples.

EXAMPLE 1 Attempted Reduction of Methyl Perfluoro(2-Hexyldecanoate)

In this example, the reduction of a methyl ester of a branchedperfluoroalkanoic carboxylic ester was attempted.

Methyl perfluoro(2-hexyl decanoate) (formulaCF₃(CF₂)₇CF((CF₂)₅CF₃)COOMe) was prepared by treatingperfluoro(2-hexyldecyl acetate) (CF₃(CF₂)₇CF((CF₂)₅CF₃)CF₂OC(O)CF₃) withmethanol in quantitative yield. Methyl perfluoro(2-hexyl decanoate) 88.0g (0.106 mole) was added to a mixture of sodium borohydride 10.0 g(0.263 mole) and isopropanol (200 ml) at 26 -28° C. After stirringovernight at room temperature, the mixture was poured into ice-water andacidified with dilute hydrochloric acid. The lower phase was separatedand analyzed by gas chromatography. It was found that the mixtureobtained was mainly the starting ester with some unidentified reactionproducts. The recovered product was added to a mixture of sodiumborohydride 10.0 g (0.263 mole), isopropanol (200 ml) and diglyme (10ml) at 45-50° C. After six hours, the reaction mixture was worked up asdescribed above to give a product mixture consisting of at least sixunidentified products and some unreacted starting ester but nonoticeable amount of perfluoro-1H,1H-2-hexyldecanol.

EXAMPLE 2 Reduction of Perfluoro(Octyl Octanoate)

Perfluoro(octyl octanoate) (8967 g, 10.78 mole) (made by fluorination ofthe corresponding ester (octyl octanoate) was diluted with Halocarbonoil 0.8™ (an oligomer of chlorotrifluoroethylene) (Halocarbon ProductsCorp.) to 50 wt percent. The mixture was added dropwise to a mixture ofsodium borohydride 657 g (17.2 mole) and diglyme (1 liter) in a stirredreactor. The reaction temperature was kept at 35° C. by external coolingand raised to 60° C. toward the end of the reaction time (about 4-5hours). The mixture was cooled to room temperature and then about 4 kgof ice was added to the mixture. The cooled mixture was then carefullydiluted with water (20 liters) with stirring, and the mixture wasacidified with dilute hydrochloric acid. The lower organic phase wasseparated and washed twice with dilute hydrochloric acid. The lowerorganic phase was then fractionated to give perfluoro-1H,1H-octanol 7589g (88% yield).

It can be seen that reduction of fluoralkyl ester of a straight-chainperfluorocarboxylic acid proceeds in good yield.

EXAMPLE 3 Reduction of Perfluoro(2-Hexyldexyl Acetate)

Perfluoro(2-hexyldecyl acetate) was prepared by the direct fluorinationof the corresponding hydrocarbon according to a published procedure(Bierschenk et al. U.S. Pat. No. 5,093,432) in 70% yield.Perfluoro(2-hexyldecyl acetate) (3307 g, 3.55 mole) was diluted withHalocarbon Oil 0.8™ (4 liters). The mixture was added to a mixture ofsodium borohydride (202 g, 5.32 mole) and diglyme (100 ml) in a stirredreactor at 30-60° C. The reaction mixture was treated with ice-water asdescribed above and acidified with dilute hydrochloric acid. The productwas fractionated under vacuum to give 2200 g (77% yield) ofperfluoro-1H,1H-2-hexyldecanol. Boiling point: 150° C./10 mmHg; Meltingpoint: 73-75° C. The analytic data of this new compound are as follows:¹H NMR: —CH₂OH, 4.4 ppm; —CH₂OH, 5.3 ppm. ¹⁹F NMR: —CF₃, −81 ppm (6F);—CF₂—, −115 to −126 ppm (24 F); —CF—, −191.5 ppm (1 F). IR (cm⁻¹): 3311(—OH); 1203, 1146 (C—F).

Thus, an α-branched perfluoralkylmethanol was produced in good yield byreduction of a perfluoralkyl ester of an α-branchedperfluoralkylcarboxylic acid.

EXAMPLE 4 Reduction of Perfluoro(Diethyl 2-Octylmalonate)

Perfluoro(diethyl 2-octylmalonate) was prepared by the fluorination ofthe corresponding hydrocarbon in 65% yield. Perfluoro(diethyl2-octylmalonate) (1632 g, 2.10 mole) diluted with Halocarbon Oil 0.8™was added to a mixture of sodium borohydride 208 g (5.47 mole) anddiglyme (500 ml) at 30-60° C. The reduction mixture was treated withice-water and then acidified with dilute hydrochloric acid. The productmixture was fractionated under vacuum to give pure2-fluoro-2-perfluorooctyl-1,3-propanediol 930 g (86% yield). Boilingpoint: 135° C./0.1 mmHg; Melting point: 145-149 ° C. The analytic dataof this new compound are as follows: ¹H NMR: —CH₂OH 4.09 ppm; —CH₂OH,4.83 ppm. ¹⁹F NMR: —CF₃, −82.2 ppm (3 F); —CF₂—, −120.3 to −127.2 ppm(14 F); —CF—, −185.4 ppm (1 F). IR (cm⁻¹): 3300 (—OH); 2900 (C—H);1300-1100 (C—F).

EXAMPLE 5 Reduction of Perfluoro(Diethyl 2-Butylmalonate)

Diethyl 2-butylmalonate (497 g (2.3 mole) was fluorinated in HalocarbonOil 0.8™. The fluorinated mixture was added to sodium borohydride 87 g(2.3 mole) suspended in stirred dimethoxyethane (3 liters). Afterreaction, the reduction mixture was carefully added to a dilutedhydrochloric acid solution and the oily product layer was separated. Theproduct mixture was fractionated under vacuum to give2-fluoro-2-perfluorobutyl-1,3-propanediol. Boiling point: 80° C./0.1mmHg.

The analytical data of this new compound are as follows: ¹H NMR: —CH₂—,4.18 ppm; —OH, 3.60 ppm. ¹⁹F NMR: —CF₃, −82.5 ppm (3 F); —CF₂—, −121.8to −127.8 ppm (6 F); —CF—, −183.1 ppm (1 F). IR (cm⁻¹): 3300 (—OH); 2900(C—H); 1300-1100 (C—F).

EXAMPLE 6 Reduction of Perfluoro(Undecanoic τ-Lactone)

Undecanoic τ-lactone 460 g (2.5 mole) was fluorinated in Halocarbon Oil0.8 ™ (2 liter). The fluorinated mixture was then added to a solutioncontaining sodium borohydride 95 g (2.5 mole) and dimethoxyethane (3liter) at 33 to 45° C. After reaction, the reduction mixture wascarefully poured into a solution of hydrochloric acid. The lower organicphase was separated and washed with dilute hydrochloric acid severaltimes. Vacuum distillation gave 544 g of pure diol, perfluoro1H,1H,4H-undecan-1,4-diol, CF₃(CF₂)₆—CH(OH)CF₂CF₂CH₂OH. Boiling point:140° C./0.1 mmHg; Melting point: 75-78° C.

The analytical data of this new compound are as follows: ¹H NMR: —CH₂—,4.10 ppm; —CH, 4.78 ppm. ¹⁹F NMR: —CF₃, −82.0 ppm (3 F); —CF₂—, −123.0to −127.6 ppm (16 F). IR (cm⁻¹): 3300 (—OH); 2900 (C—H); 1300-1100(C—F).

EXAMPLE 7 Reduction of Perfluoro(Dodecanoic δ-Lactone)

Dodecanoic δ-lactone 460 g (2.32 mole) was fluorinated in Halocarbon oil0.8™ (6 liter). After most of the solvent was removed by distillation,the crude perfluoro(dodecanoic δ-lactone) mixture was added to asolution containing sodium borohydride 88 g (2.32 mole) anddimethoxyethane (2 liter) at 33 to 45° C. The reduction product wascarefully hydrolyzed by pouring the reduction mixture into a solution ofdilute hydrochloric acid. The lower organic phase was separated andwashed several times with dilute hydrochloric acid. Vacuum distillationgave 300 g of pure diol, perfluoro 1H,1H,5H-dodecan-1,4-diol,CF₃(CF₂)₆—CH(OH)CF₂CF₂CF₂CH₂OH. Boiling point: 145° C./0.1 mmHg; Meltingpoint: 88-91° C.

The analytical data of this new compound are as follows: ¹H NMR: —CH₂—,4.00 ppm; —CH, 4.80 ppm. ¹⁹F NMR: —CF₃, −82.0 ppm (3 F); —CF₂—, −122.3to −128.0 ppm (16 F);. IR (cm⁻¹): 3300 (—OH); 2900 (C—H); 1300-1100(C—F).

EXAMPLE 8 Surface Coating with Branched Perfluoralkyl Methanol Polymers

The compound produced in Example 4, supra, can be employed to provide adurable, low-friction surface coating. The compound,perfluoro-1H,1H-(2-hexyldecanol), is converted to the acrylate ester bytreatment with acryloyl chloride in the presence of a suitable tertiaryamine base, such as triethylamine. The perfluoro-1H,1H-(2-hexyldecanol)acrylate is then coated onto a surface, such as a primed metal surface,and the acrylate moieties are polymerized, e.g., with a radicalinitiator or UV radiation, to provide a durable surface coating of anacrylic polymer substituted with branched-chain perfluoroalkyl chainsalong the backbone.

Those skilled in the art will recognize, or be able to ascertain usingno more than routine experimentation, many equivalents to the specificembodiments of the invention described herein. Such equivalents areintended to be encompassed by the following claims. The contents of allpublications and patents cited herein are hereby incorporated byreference.

1. A perfluorocarbon dimethanol compound represented by the formulaR_(f)—C(R′_(f))(CH₂OH)₂, wherein R_(f) is a perfluorocarbon moiety, andR′_(f) is fluoride or a perfluorocarbon moiety, wherein R′_(f) and R_(f)may be independently substituted by a halogen, hydroxyl, alkyl, alkoxyl,cyano, azido, heterocyclyl, aralkyl, aromatic, or heteroaromatic moiety,or perfluorinated derivatives thereof.
 2. The compound of claim 1,wherein R_(f) is a perfluoroalkyl moiety, wherein R_(f) may besubstituted by a halogen, hydroxyl, alkyl, alkoxyl, cyano, azido,heterocyclyl, aralkyl, aromatic, or heteroaromatic moiety, orperfluorinated derivatives thereof.
 3. The compound of claim 1, whereinR′_(f) is fluoride.
 4. A perfluorocarbon dimethanol compound representedby the formula R_(f)—CF(CH₂OH)₂, wherein R_(f) is a perfluorocarbonmoiety, wherein R_(f) may be substituted by a halogen, hydroxyl, alkyl,alkoxyl, cyano, azido, heterocyclyl, aralkyl, aromatic, orheteroaromatic moiety, or perfluorinated derivatives thereof.
 5. Thecompound of claim 4, wherein R_(f) is a monovalent, perfluorinated,alkyl or alkenyl organic radical having one to twenty carbon atoms,wherein the radical can be interrupted by divalent oxygen or sulfuratoms and may be substituted by a halogen, hydroxyl, alkyl, alkoxyl,cyano, azido, heterocyclyl, aralkyl, aromatic, or heteroaromatic moiety,or perfluorinated derivatives thereof.
 6. The compound of claim 4,wherein R_(f) is a perfluoroalkyl moiety, wherein R_(f) may besubstituted by a halogen, hydroxyl, alkyl, alkoxyl, cyano, azido,heterocyclyl, aralkyl, aromatic, or heteroaromatic moiety, orperfluorinated derivatives thereof.
 7. The compound of claim 4, whereinR_(f) is selected from the group consisting of trifluoromethyl,pentafluoroethyl, heptafluoroisopropyl, 2-trifluoromethoxyperfluoropentyl, perfluorocyclopentyl, wherein R_(f) may be substitutedby a halogen, hydroxyl, alkyl, alkoxyl, cyano, azido, heterocyclyl,aralkyl, aromatic, or heteroaromatic moiety, or perfluorinatedderivatives thereof.